Across:
   1. Developed "A to Z" about phosphorus and aluminium based mineral (5)
   4. Statesman delicately contacting leaders of eastern regime (9)
   9. Chaos after nasty rut wrecked limo (7)
  10. Mostly reliant, in turning, on this part of airplane's wing (7)
  11. Who 25 met in 22's tangled maze: no God, but a revered human (3 6)
  12. No time to strike out for 24 on the slide (5)
  13. "Dear Sir," this letter starts, with reserve all round (6)
  14. On 25s itinerary in 22: 5 down (from 2nd to 5th) and 3 down (briefly) (8)
  17. Billy and cup used for brew in outdoor setting (8)
  19. Wrote date on food tubes (6)
  22. see 25 down
  24. Statesman taking liquor for gallery as he is a player (9)
  26. Had psychedelic experience, with time shredded (7)
  27. Stand to speak 17, thus leading a lead animal (7)
  28. Loves being among amazing glitter of Italian opera (9)
  29. King, plagued with regrets, seen finally gain wisdom (5)
Down:
   1. Celtic Jayson with hissy fit after losing finals in lean year (5)
   2. Mindlessly repeats back some pastor, rapping (7)
   3. Statesman's zeal had overseas US envoys noticing land and its leaders (4 5)
   4. He was here so many times ... at heart, mayor liked coming back (6)
   5. On 25s itinerary in 22, far removed from Ashraf Ghani mess (8)
   6. Less bothered by 22 across essentially creating bits of land at sea (5)
   7. Carefully sharing extra little bit of food (7)
   8. A little car trouble? (9)
  13. Limit airconditioner, having it or a little bit of electronics (9)
  15. Cleverly grew a tall 22 landmark (5 4)
  16. Social news site had slots free (8)
  18. Wicked 'gin' jibe was capital (7)
  20. Country hands both dismissed when animal rib broken (7)
  21. see 25
  23. Program gansgter to horrify (5)
  25,21,22ac. New president turned on leaders of government over eastern state, tired of cold hostility, in a pivotal sort of moment  (5 4 2 5)